The present invention relates to the thermal processing of glass sheets, and, particularly, to their processing while suspended from tongs for conveyance along a first path of glass sheet travel through a heating furnace, a fluid application station and into a transfer station where the glass sheets are transferred to a conveyor defining a second path of glass sheet travel. Mass production facilities for tempering glass sheets or shaping and tempering glass sheets require that the glass sheets be conveyed in a series through a tunnel-shaped heating furnace, be transferred one at a time to a shaping station, be shaped to a desired shape and transferred to a fluid application station where blasts of cold tempering medium such as cold air blasts are applied against the opposite surfaces of the shaped glass sheet. The conventional commercial operation involves processing one glass sheet at a time first at the shaping station and then at the fluid application station while a previous glass sheet in the series is suspended by tongs at a parking station beyond the fluid application station to enable the glass sheet to cool sufficiently before the tongs are relaxed to transfer the glass sheet to the conveyor defining the second path of glass sheet travel.
In a particular commercial arrangement, the second path of glass sheet travel comprises a so-called "peg-type" conveyor which transfers glass sheets in a direction transverse to the first path of glass sheet travel. Tong-supporting carriages carry tongs which grip the glass sheets during their movement along said first path of glass sheet travel through the heating furnace, the fluid application station and the parking station and into a glass sheet transfer station. At the latter station, the tongs are relaxed to release the glass sheet from gripping by tongs into a position along the second path of glass sheet travel where the lower ends of said released glass sheets rest on bumpers attached at one end to transverse slats interconnecting transversely spaced chain drives of a peg conveyor for supporting glass sheets between sets of pegs extending upward from said slats and spaced sufficiently from adjacent sets of pegs to form spaces to permit a glass sheet released from tong gripping relation to drop between adjacent sets of pegs of the peg conveyor.
Unfortunately, when a glass sheet is suspended from tongs at the parking station awaiting entry into the transfer station, it tends to sway because of fluid applied against the opposite surfaces of curved glass sheets supported by tongs at the fluid application station. When the glass sheet is transferred from the parking station to a position over a space between adjacent sets of pegs extending upwardly from the peg conveyor slats and bumpers, occassionally a glass sheet would not deposit properly onto the slats or would sway away from a freely hung position. This swaying causes the leading edge of a swaying glass sheet to collide with one or the other of the upstream pegs of the adjacent sets of pegs instead of dropping into the space between adjacent sets of pegs when the tongs are relaxed. Such a collision sometimes causes the glass sheet to fall on the floor of the plant and provide a problem of glass sheet removal instead of transferring the processed glass sheet onto the second path of glass sheet travel. Falls of this nature sometimes result in breakage of a processed glass sheet which represents a considerable investment in materials, labor and time of use for expensive equipment.
In the past, sliding doors had been provided at the exit of the furnace to protect the furnace from heat loss and the glass sheets within the furnace from premature cooling due to flow of cold fluid from the fluid application station through a shaping station, if present, and into the exit end of the furnace, or directly from the fluid application station into the furnace through its exit in case the apparatus was designed for treating flat glass sheets without shaping. Also, moving gates have been provided between the shaping station and the fluid application station in so-called vertical press bending and tempering apparatus wherein the gates protect the downstream portion of the shaping station from differential cooling due to deflection in an upstream direction toward the shaping station of cold tempering medium blasted against the shaped glass sheets. The presence of these gates in the positions normally occupied in prior art apparatus did not prevent the swaying of glass sheets suspended by tongs in positions along said first path of glass sheet travel located downstream of the fluid application station. Hence, glass sheets were frequently lost at the transfer station where the processed glass sheet was released from tong gripping in an attempt to transfer said sheet onto said peg conveyor between adjacent sets of upwardly extending pegs.